Tungsten-containing films are used in multiple applications for semiconductor device fabrication. For example, metallic tungsten is the primary conductor for contacts and vias. Although the typical film stack in use today is PVD-Ti/CVD-TiN/W nucleation/CVD-W, tungsten nitride's relatively low resistivity, good adhesion to dielectric films, and good diffusion barrier properties makes it desirable as a replacement for Ti/TiN. Standard tungsten nitride CVD techniques adequately fill low aspect ratio features, while for higher aspect ratios, pulsed nucleation layer (PNL) techniques may be used. Both CVD and PNL processes involve exposing the partially fabricated semiconductor device to a tungsten precursor (typically tungsten hexafluoride (WF6). Conventional CVD involves the simultaneous introduction of gas phase reactants, including the tungsten precursor (typically tungsten hexafluoride (WF6)) and a nitrogen containing gas (e.g., N2), near a heated wafer surface. PNL techniques typically involve reacting the tungsten precursor with an adsorbed layer of a reducing agent to form a metallic tungsten layer, then nitriding this layer.
One difficulty in replacing Ti/TiN with WN on silicon is that the WF6 precursor commonly used to deposit WN may attack the silicon, forming defects. Deposition of other tungsten-containing layers on silicon presents the same difficulties.
What are therefore needed are improved methods for depositing tungsten-containing layers on silicon that reduce or eliminate defects in the silicon.